Flashlights are conveniently sized battery powered portable light sources, which provide the user with a source of illumination. Said illumination could be white light or light of a specific color, or even light outside the visible range of wavelengths, such as ultraviolet or infrared radiation. The “color” or wavelength of the light will depend on the nature of the light source or light sources used in the flashlight. These would typically be either tungsten lamps, ARC lamps, light emitting diodes (LEDs), lasers, or any other emitter.
Because of the general nature of flashlights and their wide range of applications, it is very desirable for a flashlight to be able to emit, at the user's direction, different levels of light output, and/or different colors or wavelengths of light. This can be accomplished using multiple light sources or a single light source, which can be adjusted to provide different levels of light output.
The principal light source used in flashlights is the tungsten filament lamp, as alternatives suffered inadequate illumination, or excessive battery consumption. Tungsten filament lamps, however, cannot be effectively used as a variable output light source because they must be operated close to their design point (current & voltage) if they are to retain their efficiency in converting electrical energy to light. Generally speaking, the same thing can also be said about ARC lamps. Thus, if one wanted two significantly different light outputs from the same flashlight, this would require the use of two different lamps. Examples of such prior art systems are described in Matthews U.S. Pat. Nos. 5,629,105 and 6,386,730, the former teaching the use of a second lamp protruding through the reflector at a point offset to the side of the main lamp which is located at the focal point of the (parabolic) reflector, and the latter teaching the use of two lamps each with its own reflector, the reflectors merged together in a manner such that the light from each lamp interacts only with its own reflector.
In such existing systems, the switching system consists of mechanical contact arrangement where the physical axial displacement of a switch system element (either by direct finger or thumb pressure or by rotation of a tail cap or head of the flashlight) causes first ene lamp to be connected to the battery, and additional applied pressure or flashlight element rotation causes the second lamp to be connected to the battery. In some cases the design is such that the first lamp is disconnected when the second lamp is connected to the battery. In other cases, the first lamp remains connected when the second lamp is connected.
In practice, such dual- or multi-source flashlights typically have a pressure switch located on the opposite end of the flashlight from the light source. This switch system, or tail cap, may be rotated through a range of angular positions, each providing a different response to application of a button on the pressure switch. Rotation of the switch on the helical threads connecting it to the flashlight body generates axial movement to move contacts toward or apart from each other. In a first position, the switch contacts are farthest apart, so that full pressure of the button has no effect. This is the “lockout” position. By rotating the switch to the second position, fully pressing the button connects the first lamp to the battery, but not the second (and usually brighter) lamp, which is controlled by more widely spaced contacts that remain locked out. In the third position, which is the position most normally used, moderate pressure on the button first connects the first lamp to the battery; greater pressure, including a “bottoming out” condition then connects the second lamp to the battery. In a fourth rotational position, the first lamp remains on when the button is not pressed and the second lamp is connected in response to additional pressure on the button or to additional rotation of the tail cap. In a fifth rotational position both lamps are connected without the application of any pressure on the button
While effective, such dual-source lights have several limitations. First, they require the user either to maintain button pressure throughout illumination, or to rotate a switch between operating modes. This requires either continuous use of one hand, or the occasional use of both hands (to rotate the switch), either of which may be disadvantageous for critical military and law enforcement applications.
When set to certain switch modes existing lights do not enable rapid illumination for emergencies. When in the lockout mode or the second mode noted above, maximum pressure will not illuminate the brighter lamp. Changing modes takes time, and requires two hands, which may be disadvantageous in an emergency.
Existing lights have limited choice of light levels. Many tasks require different illumination levels. The moderate level of illumination provided by the first lamp (LED) for many tasks such as camping and ordinary trail navigation may be much brighter than would be desired for map reading in critical military situations. Other applications may require still different moderate lights levels when the full brightness (and shorter run time) of an incandescent lamp is not suitable. Moreover, there is a substantial range of possibly desired brightness levels between the maximum of the first lamp and the full brightness of the second lamp that are not obtainable.
It should be noted that the term “lamp” is used in its most general meaning, namely that of any light source (which could be a tungsten filament lamp, an LED, or an ARC Lamp) of any wavelength.